1. Field of the Invention
The present invention relates to a ball chain, and more particularly to a ball chain that is used in a linear guideway, and both ends of the chain are radially mated each other, such arrangement can suppress axial rotation of the ball chain and can improve the operating smoothness of the ball chain.
2. Description of the Prior Art
Referring to FIG. 1, which shows a chain structure 8 that is used in linear guideway to connect a plurality of balls in series. The chain structure 8 includes a plurality of spacers 81 used to separate two neighboring balls 7, and two connecting members 82 are arranged in the axial direction of the chain structure for connecting the plurality of spacers 81 together in series. Each of the spacers 81 is defined with a spherical concave 811 for mating with the balls 7, so that the balls 7 can be retained between two spacers 81.
Referring to FIGS. 2 and 3, a linear guideway 9 comprises a rail 91, a sliding block 92, and two end caps 93 installed at both ends of the slide block 92. In the rail 91 is formed a plurality of ball rolling tracks 911, and the sliding block 92 is defined with a plurality of ball grooves 921 corresponding to the ball rolling tracks 911, and a plurality of circulation passages 922 provided for circulation of the balls 7. In each of the end caps 93 is formed a return path 931 for jointing the circulation passages 922 to the grooves 921, so as to form an endless circulation path for the balls 7.
Since the connecting members 82 protrude out of the balls 7, the sliding block 92 should be defined with receiving grooves for receiving the connecting members 82. In order to facilitate manufacture, the sliding block 92 is usually drilled with a through hole 923 in which an injection-molded plastic pipe 94 is received. Then the circulation passages 922 and the receiving grooves 941 for receiving the connecting members 82 are formed in the pipe 94. Furthermore, the return path 931 is also formed with a groove 932 (as shown in FIG. 4) for receiving the connecting members 82, so that the groove 932 and the receiving grooves 941 can be used to accommodate the connecting members 82, during the movement of the balls 7 and the chain 8.
An ideal chain should be shaped in the form of a circle whose length is the same as the length of the path formed by the ball grooves 921, the circulation passages 922 and the return path 931. However, in real application, it is difficult to make a seamless circular chain, therefore, the chain is usually made in the form a long and narrow chain, and then both ends of the chain are connected together, forming a circle. For example, JP Pat. Nos. 05-52215 and 05-52216 disclose a long narrow chain, at both ends of the chain is arranged a connector for jointing the two ends of the chain together.
However, in order to improve the precision and hardness of the reciprocating motion of the sliding block relative to the rail, it is necessary to change the diameter of the balls so as to produce a pre-pressure, then the purpose of the improving the precision and hardness can be achieved.
When assembling the both-end-connected chain in the sliding block, if first time assembled balls are too large or small to produce an expected pre-pressure, it needs to slice off the already-connected connectors at both ends of chain, then all the balls can be taken out of the chain and the chain should be reloaded with new balls, and then the chain and the new balls should be reassembled in the sliding block for test, until the size of the balls can produce the expected pre-pressure. Such process is very inconvenient.
To overcome the above problems, some people in the art proposed a design in which the outer end of the spacers at both ends of the chain is formed with a concave for mating with the shape of the balls. And in assembly, a buffering ball (disclosed both in JP Pat. Nos. 05-52217 and 06-72612) is additionally disposed between both ends of the chain and received between the concave of the spacers at both ends of the chain.
Besides, some people in the art proposed a chain structure that has no connectors at both ends thereof so as to overcome the assembly problem of the both-end connected chain. For example, JP Pat. No. 10-9264 discloses such a chain structure that has no connectors at both ends thereof, so that an interval will be left between both ends of the chain after the chain is assembled in the sliding block.
However, the chain with an interval left between both ends thereof will form a free end at the both ends, it will cause a problem that the protruding spacers at both ends of the chain will impact the wall of the return path. The continuations of JP Pat. Nos. 10-318257 and 11-2241 have pointed out this problem, and in order to solve it, the both ends are designed to have an axial concave shape and a convex shape, so that the two ends of the chain can be axially engaged with each other, solving the problem of JP Pat. No. 10-9264.
Since the sliding block 92 is made of metal, and the ends caps 93 are made of plastic injection molding, it will have fitting tolerance between the sliding block 92 and the end caps 93. The value of the tolerance is usually determined by whether the balls are able to smoothly pass through the conjunction between the circulation passage 922 and the return path 931. However, the size of the receiving grooves 941 and the concave 932 are much smaller than the circulation passage 922 and the return path 931, the allowable error of the circulation passage 922 and the return path 931 is probably a considerable error as compared to the receiving grooves 941 and the concave 932. In other words, such an error will form comparatively large level difference at the conjunction between the receiving grooves 941 and the concave 932. As shown in FIG. 4, such a level difference will interfere with the passage of the connecting members 82.
The chains disclosed in the aforesaid JP Pat. Nos. 05-52217, 10-9264, 10-318257, 11-2241 and 06-72612 are long and narrow, therefore, both ends of the connecting members 82 are separated no matter the two ends of the chain 8 are connected. And the chain will be pushed, pulled and distorted constantly when it drives the balls to move, therefore, it will have a problem of axial distortion of the chain. Once it occurs, the connecting members 82 in two receiving grooves 941 will be slanted and located at different heights. Both ends of the aforementioned various chain structures are axially connected, and the problem of radial distortion cannot be solved. Therefore, the distortion of the chain will form a force pushing one of the connecting members 82 to impact the conjunction of the receiving groove 941 and the groove 932, as shown in FIG. 4. As a result, the chain and the balls cannot move smoothly. And in order to make the chain move smoothly, this problem must be solved.
In addition, regarding the JP Pat. Nos. 05-52217, 10-9264, 10-318257, 11-2241 and 06-72612, in production of the chain, initially, it should set the balls coated with grease in the mold, and then the chain can be formed by injection molding, therefore, the respective spacers 81 in the formed chain will form a concave 811 corresponding to the shape of the balls 7. In other words, the balls 7 will be in a surface contact relation to the concave 811 of the spacers 81, this will increase the rolling friction of the balls, causing unnecessary momentum waste. This problem also needs to be improved.
The present invention has arisen to mitigate and/or obviate the afore-described disadvantages.